First MDMA Cap - Black out :(?

So i had my first bad experience the other night. I drank a little bit then head out with friends. Took one MDMA cap. Within half hour i just remember starting to trip/feeling off then i "came to" when the paramedics pricked my finger outside the club!!!! I have no recollection but I was told that i sat on the ground, refused to move, just licked the air :S I have taken them before and have also drunk on them .... can anyone suggest what could have made me black out??? Is there a big difference between the caps and pills - i have dealt more with pills... not so many caps.